During the spin cycle of the washing machine, when water is removed from wet clothes centrifugally by spinning the clothes in a spin basket, it is important that the washing machine lid remains closed to prevent injury to the user. For this reason, the lid is normally connected to an electrical switch which controls a mechanism to stop the motion of the spin basket when the lid is raised.
For reasons of manufacturing convenience, it may be desirable to place the lid switch near the lid hinge. At this position, however, there is very little motion of the lid when the lid is opened. As a result, the lid switch must be carefully adjusted during manufacturing to ensure that the spin basket is stopped before the lid is opened too far. This adjustment may be accomplished, for example, by mounting the lid switch to a slide adjustment bracket, which is manually located and tightened into position with one or more screws. This adjustment process increases the cost of manufacturing the washing machine and creates the potential for future misadjustment if the screws become loosened.
Referring now to FIGS. 2 and 3, a prior art lid switch assembly 30 disconnects the motor 32 of the washing machine 10 from AC power 34 when the lid 20 is opened by more than a predetermined amount such as might allow access to the tub 12 while it is in motion. A first, normally-open switch 36 provides load contacts placed in series with the motor 32 (between the AC power 34 and the motor 32) so that when the contacts of switch 36 are open, the motor 32 is stopped. Switch 36 is activated by a cam follower assembly 38, which includes a rounded pin 40 extending through the rear vertical wall of the recess 19 to ride against the cam surface 22 of the lid 20. When the lid 20 is closed, the cam surface 22 is configured to push the pin 40 rearward in through the flange forming recess 19. A spring 46 biases the pin 40 toward the cam surface 22. This prior art of the cam follower is described generally in U.S. Pat. No. 3,569,646 issued Mar. 9, 1971, hereby incorporated by reference.
A pivoting metal arm 42 is attached to the pin 40 and includes an angled upward finger 44 extending through the top 18 of the washing machine 10. When the lid 20 is closed, the finger 44 pushes in the operator of the switch 36 to close its contacts allowing power to be received by the motor 32. Arm 42 and finger 44 are biased upward against the pin 40 by the same spring 46 which biases pin 40 toward the lid 20.
When lid 20 is raised by a small amount still preventing access to the tub 12, the cam surface 22 is configured to permit forward movement of the pin 40, the arm 42, and finger 44, releasing the operator of the switch 36 and breaking the circuit to the motor 32. Further opening of the lid 20 to a vertical position, causes additional forward movement of the pin 40 and finger 44 (to a position indicated by 44') until it compresses an operator of a second switch 48, opposing the operator of switch 36 causing the normally-open contacts of that switch 48 to close.
As shown in FIG. 2, contacts of switch 48 are placed in series with a fuse 50 and the series combination placed to shunt the motor 32. Further, the contacts of switch 48 alone shunt a valve 52 providing control of water to the tub 12. Normally, when the lid 20 is in the fully raised position and the contacts of switch 48 are closed, the contacts of switch 36 will be open and thus no current will flow through the series combination of the fuse 50 and the switch 48. On the other hand, if the contacts of switch 36 are welded closed, as may occur upon failure of switch 36, then when the lid 20 is fully opened and the contacts of switch 48 close, current flowing from the source of AC power 34 through the welded closed contacts of switch 36 through fuse 50 and closed contacts of switch 48 to ground will be sufficient to blow fuse 50. When fuse 50 blows, valve 52 will no longer operate signaling the user to call a service technician who will replace switch 36.
It should be noted, however, that the motor 32 is never disabled and thus, there may occur situations when the user is not prevented from opening the lid while the tub is rapidly rotating during the spin cycle. Generally, it is not practical to place fuse 50 in series with both the motor 32 and the valve 52 (for example, between AC power 34 and the switch 36) because the high peak demands of the motor 32 would require the fuse 50 to be extremely large and slow acting which would compromise the ability of current through switch 48 to reliably trip the fuse 50 without conducting dangerously high currents.
Generally other contacts are in series with both the motor 32 and valve 52 as controlled by the washing machine timer. These contacts are omitted for clarity in this and subsequent schematics.
Referring again to FIG. 3, the metal arm 42 is also pivotable about an eyelet 54 on the bottom of pin 40 so as to move finger 44 out from between the operators of switches 36 and 48, upon forward pressure on a downwardly extending hook 56 on the far side of finger 44 with respect to eyelet 54. This forward pressure may be applied when hook 56 is struck by the wall of the tub 12 when an out-of-balance condition causes motion of the tub 12 forward as indicated by arrow 58. When tub 12 presses against hook 56, the entire arm 42 is pivoted downward as indicated by arrow 60, removing it from contact with switch 36 and causing the motor 32 to be disconnected until the lid 20 is lifted to correct the out-of-balance condition by rearranging of the clothes within the tub 12, and the finger 44 is drawn back between the operators of switches 36 and 48.
Switches 36 and 48 are held on a carrier plate 43 attached to the top 18 by self-tapping screws 45 received by slots within the carrier plate 43 so that the assembly of switches 36 and 48 may be moved forward or backward so as to properly locate each switch 36 and 48 to be actuated with a predetermined opening and closing of the lid 20, as described above. This adjustment requires both the proper positioning of switch 36 to ensure that the washing machine 10 is deactivated with minor opening of the lid 20, and the proper positioning of switch 48 to ensure that the contacts of switch 36 are "tested" with complete opening of the lid 20. As has been noted, these additional adjustment steps during manufacturing increase the cost of the manufacturing process and carry with them the possibility of future misadjustment if screws 45 are loosened during use.